The proposed research continues the current investigation of how chromosomes are arranged in somatic nuclei. Investigations supported by the current grant suggest that there is a specific arrangement of both homologous and nonhomologous chromosomes within nuclei and that chromosome ends play an important role in the establishment and maintenance of these associations. The current proposal continues examination of these arrangements and seeks to answer such questions as when are homologous chromosome associations first established and how important are chromosome ends in this process. There is a major shift in emphasis in the current proposal from the role of somatic chromosome associations as they may relate to meiotic pairing, to the more direct role they may play in somatic cells themselves. The prime question being raised is "Does disruption of the normal arrangement of chromosomes in somatic nuclei lead to an increased frequency of translocations and thereby indirectly to cancer?" The approach proposed is a cytological examination of: 1) homologous exchanges and 2) translocation frequency when a chromosomal breaking agent (such as mitomycin C) is administered to cells at the same time as a chemical demonstrated to disrupt somatic associations (colchicine). If an increase in translocation frequency is demonstrated, a simple series of cytological tests to screen other chemicals for this activity will be developed.